Add the config gem to Configuration_Management.yml

[hosamaly]

Add the config gem to the Configuration Management category.

---

Thanks for contributing to the Ruby Toolbox catalog! <3

Before submitting your pull request:

• If you're referencing a gem by its GitHub repository (e.g. rails/rails), please verify
  that it is not packaged as a Ruby gem. (If it is packaged as a gem, please reference it
  by its gem name instead, e.g. rails.)
• Please make sure the projects are listed in case-insensitive alphabetical order
• Make sure the CI build passes, we validate your proposed changes in the test suite :)

[colszowka]

How could we not have a gem with such a name in that category yet :) Thanks @hosamaly